In the past, olefin homopolymers and copolymers have been used for a wide variety of applications, e.g., as insulation for electrical cables, wires and other electrical apparatus and as coatings for metals. Polyolefins are especially suitable for such applications because of their flexibility and high resistance to stress-cracking, and thermoembrittlement.
The polyolefins, however, are susceptible to oxidative degradation which is promoted by heat and ultra-violet light. Such degradation is further enhanced by metals which may be in intimate contact with the polymer or present within the polymer as an impurity.
Copper and its alloys, iron and certain other active metals including cobalt, manganese, nickel and chromium have particularly detrimental effects on the stability of olefin polymers. Such metals promote a catalytic degradation reaction in the polyolefins which cause the polymers to become brittle and to lose strength to the extent of mechanical failure.
Polyolefins are frequently reinforced with inorganic and mineral fillers, for example, asbestos, talc, clay, silica or the like. Such fillers usually contain metals as impurities, and the fillers, therefore, exert a catalytic effect on the oxidative degradation of the polyolefins. For example, the iron impurity in asbestos fillers has proved to be particularly detrimental to asbestos-reinforced polyolefins.
In copper cable coated with polyolefins, metal catalyzed degradation presents a particular problem. In such cables, the interstices between individual wires are filled with petroleum jelly to protect the wires from any water seepage through the polymer coating. The petroleum jelly surrounding the wires, however, tends to extract stabilizers from the polymer coating. The petroleum jelly thus reduces the availability of the stabilizers for metal deactivating purposes, and consequently, decreases the stability of the polymer coating.
In the past, various antioxidant and ultraviolet light stabilizers have been incorporated into olefin homopolymers and copolymers to inhibit normal oxidative degradation. In addition, whenever the polymer might contact metals or contain metal contaminants from fillers or other additives, various metal deactivators have also been added to the polyolefins.
A number of metal deactivators are known in the art. British Pat. No. 974,274 discloses that oxamide derivatives containing the radical ##STR1## exhibit copper deactivating properties in polyolefins. Polymers and copolymers of oxamide and derivatives thereof are also discussed in the patent as being metal deactivators. Other metal deactivating oxamides having N-heterocyclic substituents are disclosed in U.S. Pat. No. 3,543,306 and in German Pat. No. 1,926,547.
Many references have recommended the use of oxalic acid derivatives as copper deactivators for various polyolefin compositions. For example, U.S. Pat. No. 3,117,104 discloses N,N'-dihydrocarbyl oxalhydrazides, where the hydrocarbyl group is selected from alkyl, aryl and naphthalene radicals. Also, U.S. Pat. No. 3,357,944 discusses oxalobis-(salicylidenehydrazide) derivatives, while U.S. Pat. No. 3,440,210 mentions N,N'-dibenzal (oxalyl dihydrazide) derivatives. Moreover, U.S. Pat. No. 3,484,285 discusses oxalyl dihydrazide and other hydrazides containing the radical ##STR2##
Still another group of compounds which have been used as copper deactivators is the substituted dicarboxylic acid dihydrazides described in U.S. Pat. No. 3,627,727 and the heterocyclic hydrazines and lactams described in U.S. Pat. No. 3,629,189.
A number of the prior art oxamide and oxalic acid dihydrazide metal deactivators display substantial drawbacks in certain polyolefin applications. Such metal deactivators cause adverse effects because of their incompatibility with antioxidants and stabilizers which are normally incorporated in the polyolefins. In such instances, the activity of the antioxidant is destroyed, and consequently, overall breakdown of the polymers occurs.
In other situations, the prior art metal deactivators do not readily disperse in the polyolefin polymer. As a result, they cannot be uniformly distributed throughout the composition.
Still another undesirable effect caused by some prior art metal deactivators is discoloration and staining. Such properties often render unsuitable an otherwise effective metal deactivator, i.e., for applications in which color stability is an important factor. For example, discoloration and staining must be avoided in decorative tiles for aesthetic reasons and in color-coded underground electrical cable insulation for reasons of identification.